This invention relates to writing or marking implements in general and, in particular, to a mechanical pencil featuring provisions for propelling successive lengths of lead without manual assistance, with a view to uninterrupted writing or marking during a change from one length of lead to another.
Mechanical pencils have been suggested in which the lead, whenever worn to a prescribed degree, is automatically propelled by the same degree. There have also been proposed those which are constructed not only for the automatic lead propelling capability but also for automatically supplying successive lengths of lead, such that when one length of lead is used up, another length of lead automatically follows for uninterrupted writing. Japanese Laid Open Utility Model Application No. 59-118580 represents an example of the second recited type of mechanical pencil.
The prior art device according to the noted Japanese utility model application comprises a lead guide movable back and forth with the lead within the pencil body, and a chuck gripping the lead against retraction (i.e. movement in a direction away from the writing end of the pencil body). Also provided are magnetic means acting between the lead guide and the chuck for opening the latter during the forward or downward travel (i.e. movement toward the writing end) of the lead guide. The next length of lead is to fall under its own weight into and through the chuck when the latter is open, and is to be gripped by the chuck when the lead guide completes its forward stroke.
Thus, according to this prior art device, the new lead has had to fall through the chuck during the very brief interval of time when it is open. There has been no guarantee that the new lead will do so, as its gravity falling through the chuck depends upon the pencil attitude at that moment.